Apparatus for thermal development of photographic materials



Dec. 27, 1966 J. H. WHITMORE APPARATUS FOR THERMAL DEVELOPMENT OF PHOTOGRAPHIC MATERIALS 5 Sheets-Sheet 1 Filed Dec. 10, 1965 INVENTOR JOHN H. WHITMORE ATTORNEYS Dec. 27, 1966 ,J wHlTMORE 3,294,947

APPARATUS FOR THERMAL DEVELOPMENT OF PHOTOGRAFHIC MATERIALS Filed Dec. 10, 1965 5 Sheets-Sheet 2 Illlllllllllllllllllllllll Ill 0 lllllllillilij llllllllllllllllllllll |\|ll.llllllllllllllllllllll 3' T I 2 l m g l I l CURVEI 5 2 1 l 8 TO I I INVENTOR TIME SEC. F168 JOHN H.WHITMORE ATTORNEYS Dec. 27, 1966 J. H. WHITMORE APPARATUS FOR THERMAL DEVELOPMENT OF PHOTOGRAPHIC MATERIALS 5 Sheets-Sheet 5 Filed Dec. 10, 1965 llll l 22 E g 9. 530m INVENTOR JOHN H. WHITMORE ATTORNEYS United States Patent 3,294,947 APPARATUS FOR THERMAL DEVELOPMENT OF PHOTOGRAPHIC MATERIALS John H. Whitmore, Binghamton, N.Y., assignor to General Aniline & Film Corporation, New York, N.Y., a

corporation of Delaware Filed Dec. 10, 1965, Ser. No. 512,973 4 Claims. (Cl. 21910.61)

This is a continua-tion-in-part of my copending application Serial No. 308,841, filed September 13, 1963, now abandoned.

The present invention relates to electrical inductive heating systems and, more particularly, to apparatus for heating strip or sheet material. It is particularly designed to provide an effective, convenient and economical means for treating strips or sheets of non-self-supporting material which is electrically non-conductive, e.g., heat developing certain types of photographic papers and the like.

A particular object of the invention is to provide an efiicient, uniform and closely controllable electrical induction heating system adapted for heating sheet materials. In particular, heat-sensitive media, including certain heat-reactive photographic sheets and films, may be treated and thereby developed. The equipment may be used for drying all types of sheet and web materials, especially those involving photographic layers, but also sheets including coatings or layers of non-image forming materials.

Various proposals have been made in the prior art for heating material by means of electrical induction heating equipment as shown in U.S. Patent 1,106,683, for example. Resistance heaters have also been used for analogous purposes.

It is also well known that high frequency electrical energy may be utilized to produce heating currents in various types of devices for the purpose of heating or drying material passing over rollers and through analogous apparatus. Examples of such devices are shown in U.S. Patents 2,761,941, 2,951,139, 2,766,362 and others.

In many cases only electrically-conductive materials may be so heated and often the material must be, to a certain extent, stiff. Also, as far as applicant is aware, the systems or devices which have been proposed in the prior art tend to be heavy and expensive, and particularly wasteful of electrical energy. This is particularly true in equipment designed for continuous or near-continuous use, where substantial amounts of energy may be required and where it is important to utilize such energy efliciently.

It is obviously desirable to provide heating equipment which would generate a minimum of waste heat. Aside from the direct economy of electric power, it is often more important to avoid the necessity of furnishing cooling accessories to operate near or adjacent to the heating device. Special cooling equipment is often required in some of the ancillary equipment of the prior art to limit undesirable temperature rise or to prevent the creation of hot spots, for example, at critical areas in a process where heat above a certain critical level cannot be tolerated.

Another object of the invention is to provide an automatic inductive heating apparatus for sheet materials, especially for developing certain photographic papers, films and the like which will require relatively little stand-by energy to maintain a state of readiness during any non-operational period. Obviously, when the material to be treated is fed intermittently, e.g., in separate sheets or strips, it is highly desirable to avoid excessive waste of energy and undesirable heating of ancillary equipment, when the developing apparatus is not actually processing the sheet material.

Further objects are to provide a versatile equipment which has the capability of continuous operation as required, but which also can operate intermittently without objectionable delay and, at the same time, without wasteful expenditure of electrical power. The apparatus of this invention is designed to operate without harmful overloading of the heating system when material is not being treated.

Ancillary objects of the invention are not only to provide all the advantages and facilities described above but, at the same time, to maintain a substantially constant operational temperature while the equipment is in either continuous or intermittent operation for heating paper, film, and the like, to uniform temperature despite extreme conditions of ambient temperature or wide fluctuations in available line voltage.

Specific and further objects include the provision of an automatic photographic processing apparatus utilizing heat energy having means for maintaining a substantially constant processing temperature for the development of photographic paper, and the like, over an extremely wide range of paper feed speeds and of ambient temperatures. At the same time, the apparatus is designed to reach its essential operating temperature quickly after a momentary or longer shut-down so that it is always ready for almost instant use. This is accomplished without waste of power while the apparatus is in stand-by usage. A particular feature of the invention is that the equipment requires no special provision for cooling adjoining parts or adjacent equipment and that the ambient conditions are essentially unchanged even when the apparatus is in full operation.

In this invention, apparatus is provided having an annular sleeve-type element for support of the usually fairly limp sheet material to be heated. This sleeve or cylinder is made of an electrically conductive material, usually sheet metal having a low specific heat and good heat conductivity. A magnetic flux-generating element is included within the cylinder and ordinarily occupies a major amount of the volume enclosed by the cylinder, that is, about 5075% or more. The flux-generating element is ordinarily coaxial with the cylinder which supports the sheet material to be heated and a fairly snug fit of the cylinder around the flux-generating element is considered desirable. Also, the guide means for the sheet material hold this material in firm, close contact with the cylinder, preferably;around almost the entire surface of the cylinder. In this way, localized heat-transfer from the cylinder to the sheet material is accomplished with relatively little production of excess heat or magnetic flux and consequent little waste of electric power. This has the advantage that the mechanical assembly of the entire machine remains relatively cool with a minimum waste of energy.

The heat transfer element, as mentioned, is in the form of a rotatable sleeve or hollow cylinder of thinwalled construction made of highly heat and electricity conductive metal, preferably copper or aluminum. The cylinder is mounted with its axis transverse to the direction of travel of the sheet material to be heated. In fact, it may be considered as a moving or rotating shorted singleturn secondary winding of an iron core transformer. The unit is designed for operation on conventional house current or public power, such as to 250 volts alternating current with a frequency of 50 to 60 cycles. The sheet material to be processed, i.e., heated, is placed preferably in direct physical contact with the heat transfer element, namely, the cylinder, the temperature of which is appropriately controlled at all times so as to avoid scorching or damaging the sheet.

The thermal energy supplied to the cylinder by resistance or ohmic heating is defined by Joules law as H=0.239I Rt, where the heat energy H is stated in calories; the current is given in amperes; the electrical resistance is stated in ohms; and the time (t) is in seconds. For equipment of this type, the resistance R is typically in the micro-ohm range and the current I is typically in the kiloampere range for most practical sizes.

By reason of its design, the equipment has low thermal capacity and still operates very satisfactorily, there being relatively small thermal losses and low specific heat in the secondary element. At the same time, after shut-down, a rapid temperature rise may be obtained with the application of sufiicient, though moderate, amounts of electrical power because of maximum exploitation of the magnetic flux produced. The time (t required by the heating element to rise from an initial room or ambient temperature T to the desired operating temperature T in degrees C. may be closely approximated by the following equation:

, c' T.T.

where time t is in seconds; the mass M of the heating element is in grams; current I is in amperes; resistance R is in ohms; and the specific heat C is a dimensionless ratio. Since the sheet material to be heated is placed in direct physical contact with the heat transfer element, i.e., the cylinder, the temperature of the heating element and the sheet material will rapidly equalize. This temperature may be continuously and automatically controlled by an electrical system.

Control equipment for this purpose may be any of several varieties which are commercially available, such as magnetic-saturable core reactors, autotransformers, and the like. The present invention preferably uses a corn-bination of controlled rectifiers and thermistor sensors for precise and economical control of the heater temperature and thus the temperature of the sheet material being processed.

Other objects and features will be apparent from the following description of the invention, pointed out in particularity in the appended claims, and taken in connection with the accompanying drawings, which are to be considered illustrative only and not limiting and in which:

FIGURE 1 is a perspective view of a preferred form of the apparatus comprising the present invent-ion;

FIGURE 2 is a sectional schematic view of the apparatus of FIGURE 1;

FIGURE 3 is a horizontal transverse section of the apparatus at reduced scale and taken substantially along the line 3-3 of FIGURE 2;

FIGURE 4 is a fragmentary sectional view of a small detail, showing the relation of the conveying belts and the material being conveyed and heated with respect to the annular inductively heated element, this view being taken substantially along the line 4-4 of FIGURE 2;

FIGURE 5 is a view similar to FIGURE 2, showing a modified form of the apparatus, this view being taken substantially along the line 55 of FIGURE 6;

FIGURE 6 is a horizontal section of the apparatus of FIGURE 5 being taken substantially along the line 66 of FIGURE 5, but with certain parts omitted;

FIGURE 7 is a side elevational schematic view of a modified form of apparatus, i.e., with a different arrangement of induction core;

FIGURE 8 is a time-temperature graph showing certain operating characteristics of the apparatus;

FIGURE 9 is a time-power consumption graph showing the power operating requirements of the equipment under various operating conditions; and

FIGURE 10 is a side elevational view of an apparatus designed for high heating efficiency and for relatively large production of materials to be heat developed.

Referring now specifically to FIGURES l, 2 and 3, power is supplied from a conventional alternating current source through lines 1 (FIGURE 2) to a primary coil or winding 2. As shown in these figures, the winding 2 is disposed about the laminated core 3 which, as shown in FIGURE 3, is in the form of rectangle and comprises two parallel main legs. This core is made separable so that it can be taken apart and inserted within the cylinder 4 which, preferably, is formed of copper and has a rela tively thin wall. Cylinder 4 fits rather snugly around a leg of the core 3, that is, the magnetic flux-generating leg of the core 3 occupies as much space as possible within the cylinder 4, usually more than half the available volume. Also, as can be seen, this magnetic flux-generating leg of the core 3 is generally coaxial with the cylinder 4, assuring passage of most of the alternating magnetic flux generated by the enclosed leg of core 3 radially and fairly evenly through the cylinder 4.

The sheet or strip material to be treated is designated generally in the drawings as 5. As can be seen, this sheet material could not be heat treated by induction without the cylinder 4, the sheet material being generally limp and not being electroconductive. In photographic applications, this sheet material may comprise a backing sheet 6 of paper or the like of which the surface coating 5 may be the photographic layer, as indicated in FIG- URE 4. In this modification the developable layer 5 is in direct contact with the rotating inductively-heated cylinder 4 so as to make the most efficient use of the heat generated. This largely avoids radiation or convection of heat beyond the paper.

The sheet material is transported to the cylinder 4 and held in close smooth uniform contact therewith by guide means which may comprise the traveling belt 7. This belt may be, and preferably is, formed of a plurality of parallel strips or segments. The segmented belt con struction is preferable because it facilitates assembly and smoothing out of the paper or film on the cylinder 4. As shown in FIGURE 1, the belt 7 in this modification comprises parallel strips or sections 7a, 7b, 7c, 7d and 7e. It is preferably fabricated from silicon rubber and fiberglass so as to have both good high temperature resistive and insulating properties. It is mounted on large rollers 16, 16, additional guide rollers 16a, 16b, 16c, etc., being provided as necessary. These rollers, appropriately journaled in the frame, surround and also support for rotation of the cylinder 4. The arrangement is such as to keep the treated sheet in continuous smooth contact with substantially the entire surface of the rotating cylinder 4 which is driven by the belt assembly. The apparatus usually will be provided with the additional sheet guide means 8 for proper feeding of the material to be treated.

A temperature measuring and control device is usually provided in the form of a smooth copper shoe 11 which is mounted on a light pressure spring leaf 12 secured to an appropriate stud of post 13 as best seen in FIGURE 2. By this means the copper shoe 11 is held resiliently against the inner moving surface of the cylinder 4, continuously sensing the temperature thereof. A thermistor element 10 of conventional type is mounted on the copper shoe 11 and a thin film of high temperature silicon grease is preferably applied to the shoe so that it serves both as a lubricating medium and a heat transfer medium between the shoe 11 and the rotating cylinder 4. By this means the temperature of the cylinder 4 may be continuously and accurately sensed. Any change in resistance of the thermistor 10, which varies with temperature, is sensed in a bridge circuit which is part of the device indicated generally at 25. The elements of this circuit are conventional and need not be described in detail. The output of the bridge may be utilized to control the current supplied to the winding 2 and, in this manner, the flux strength, the induced current and, consequently, the temperature of cylinder 4 is controlled.

A manually-adjustable control device 26 determines the operating temperature set point T This temperature is indicated on the graph of FIGURE 8. A switch 27 connects this device to controller 25. If desired, the switch may be closed to provide an optional, fixed standby temperature, say at a predetermined value T for continuous operation. In effect, closing the switch 27 disconnects the variable temperature controller 25. Electrical power is supplied at suitable voltage from the supply line receptacle 21 and fuse 22 under control of a microswitch 23 to the power input 24. The microswitch 23 may be one which is adapted to be closed by the photographic paper or equivalent sheet material entering the exposure section of a combined printing and developing apparatus when the equipment is to be employed for thermo-photographic copying. For example, in office duplicating usage, when the paper enters a thermodiazo copying machine (not shown), which machine is normally placed adjacent or may comprise a physical part of the same structure as the heating equipment of this invention, the switch 23 will be closed by the sheet material to activate the heating equipment. The means for accomplishing this are not shown, being obvious to those skilled in the art. An indicator 28, attached to controller 25, provides a visual signal, such as a light indicating that cylinder 4 has reached the set or desired temperature T after closure of switch 23. The time interval required for this heating depends on various factors, particularly the thickness of the copper cylinder wall 4. For a practical economical operation, this time interval is normally and preferably in the range of about 1 to 4 seconds, and preferably within the range of about 2 to 3 seconds. To make the time interval much shorter may require excessive expenditures of power whereas substantially longer delays may be quite undesirable for efiicient operation.

A thermostatic switch 14 also is provided which will automatically shut off the current supplied to the system in case the thermostatic control fails or, for some other reason, the cylinder 4 reaches an excessive temperature. A heat absorber 18 is placed adjacent the thermal switch 14 so as to minimize the thermal response time thereof.

In order to further reduce interior heat losses from the cylinder 4, baffles 9 are provided at the sides of the web or sheet material and the cylinder 4. In addition, a polished radiation shield 30 is preferably provided to reduce heat transfer by radiation from the cylinder 4. The core arms, both without and within cylinder 4, are wrapped with a polished aluminum foil cover to reduce heat transfer from the heated cylinder 4.

The magnetic core 3 preferably is a high eflic ency, tape-wound, grain-oriented, high-permeability, silicon steel unit. Such cores are commercially available, i.e., Hipersil C produced by the Westinghouse Electric Company. These laminated cores offer high magnetizing levels. The core, as previously mentioned, is advantageously made in two separable sections with the individual lamina junctures being staggered to provide a lapped joint when the unit is assembled. Thus it may be taken apart for insertion, both into the cylinder 4 and into the winding 2. This construction, or one closely analogous, is well known in conventional transformers.

To hold the core in proper assembled position, a stainless steel band 19, with conventional tens oning and fastening device 20, is provided to form a rigid core structure of low magnetic reluctance and low power loss. This helps to minimize heat as well as power losses.

Referring to FIGURES 8 and 9, these illustrate in general the performance of the embodiments shown in the figures of the drawing. When heating is initiated from an ambient room temperature T or from a stand-by temperature T respectively, a small temperature overshoot T T may result when power is first turned on, as indicated in FIGURE 8. This overshoot, however, is limited to only a few degrees because of the rapid control response and the low thermal inertia of the system. Temperatures of the heating element and of the heated material and the heat transfer medium, as well as that of the temperature sensor 10, are essentially coplanar and uniform because of the excellent stability of the system. In FIGURES 8 and 9, the time bases are identical. Time t represents temperature rise time and the slopes of the curves in FIGURE 8 are, in effect, functions of the power rates shown in FIGURE 9. A large rise time power rate P FIGURE 9, may be reduced substantially, to a level P for example if a small, continuous power rate P can be tolerated. In other words, a small amount of heat continuously applied may be economical for some purposes and the controls may be appropriately modified for this purpose, as will be obvious to those skilled in the art. Thus by operation of the switch 27 (FIGURE 2), the cylinder 4 may be maintained at a moderate stand-by temperature (T The power level P is maintained while the paper or film is being fed towards the cylinder 4, the latter meanwhile being raised to the operating temperature T The power level decrease from P to P (FIGURE 9) represents the automatic reduc tion in power after the paper leaves the cylinder 4. By opening switch 23, the applied power is reduced to zero unless the stand-by condition is desired. In this event, the power is reduced only to the rat-her low level P The thermistor device 10 and the shoe assembly 11, 12 are preferably placed at a location on or within the cylinder 4 near the point where the sheet material enters the system. This decreases the control loop response time. In this respect, the drawings are only diagrammatic. Representative system input power levels, cylinder 4 currents, cylinder 4 dimensions and temperature rise times may be varied, obviously, to suit the particular requirements. For example, if cylinder 4 is made 12 inches long and 2 inches inside diameter (3.14 square inches in cross-sectional area) and has a wall thickness of 0.040 inch, being fabricated of hard drawn seamless copper or of beryllium copper tubing, the circular resistance is approximately 8.9 10- ohms; that is, 8.9 micro-ohms. Circulating current in such a device, with a typical power input, may be of the order of 3.75 10 amperes which is required to raise the cylinder operating temperature from a temperature T of 86 F., starting at t or zero seconds to the operating temperature T of 350 in a time t of two seconds. The induced voltage in cylinder 4 is approximately 3.35 l0 volts. Hence the input power level P is approximately 12.6 kilowatts.

Now if the cylinder wall thickness in the above example is reduced to 0.010, other dimensions being maintained, and the time I is extended to 3 seconds, then the desired set or operating temperature T can be obtained with a much smaller input power level. The circulating currents in cylinder 4 are smaller, for example, about 7.9x l0 amperes, at an induced voltage of about 2.82 l0- volts. The circular resistance, however, has increased to 3.57 10- ohms and the power level P; has been decreased from 12.6 kilowatts to about 2.22 kilowatts. The line voltage power levels and the line current values at either voltage can be substantially reduced even below these levels by either increasing the temperature T 2 rise time t or by utilizing a low stand-by temperature T and power level P Where stand-by time is limited, the latter expedient obviously is more desirable. If stand-by time is a substantial part of operating time, it may be preferable to tolerate a moderate increase in the temperature rise time, to thereby economize on power.

Performance of the type obtained above on the equipment, having the specific dimensions indicated in the example shown above, may be obtained at a relatively low core magnetic induction level of about 9.7 10 gausses. Such a flux density produces small excitation and small losses in the copper coil 2, the latter being about 86.4 watts at maximum power level P This loss is considerably reduced for steady state operation at levels P and P The tape wound core 3, in a typical situation, has a cross section of about 1.3 inches in each direction and an effective loop length of approximately 33 inches. These dimensions apply to heating equipment having a 12 inch long cylinder as suggested in the specific example above. It will be noted that in this situation the cross-sectional area of the flux-generating element is 1.69 squ-are inches, which is more than half the 3.14 square inches cross-sectional area available within the cylinder.

Referring now to FIGURES 5 and 6, there is illustrated an apparatus having higher power and higher heating capacity characteristics than that of FIGURES 1, 2 and 3. In this figure the same reference numbers are applied to the cylinder and coil and to other common elements. The coil 2, in this case is distributed over both legs of the core with one section thereof indicated at 2 inside the cylinder 4. In other respects the apparatus is essentially the same as previously described. By having part of the coil as well as the core inside of the cylinder, the current induced within the hollow cylinder 4 may be substantially increased to give a higher temperature rise rate and also to give higher maximum surface temperatures when desired. This results from improved electromagnetic flux linkage. It also will be seen in this embodiment that the flux generating element within the cylinder comprises the combination of core and windings 2' and that this magnetic flux generating element occupies more than half the volume or cross-sectional area within the cylinder.

, Referring now to FIGURE 7, an arrangement is shown wherein the coils are external but two cores are used with double cores inside the cylinder 34. The outer iegs of the cores pass through other cylinders 36a. By this means, a greater magnetic energy is concentrated in the core sections lying within the cylinder Also, the flux generated by the outer core sections is exploited by conversion to electric current and consequent heating of the outer cylinders 36a which then contribute this heat to the central cylinder 34. This better utilization of magnetic lines of force can be calculated from the voltage in the outer cylinders, this induced voltage in the cylinders being, of course, directly proportional to the total number of Maxwells or magnetic lines passing through them. In this arrangement the paper feeding system is modified somewhat, a continuous thin metallic belt 35 passing around the cylinder 34. Alternately, if desired, the cylinder 34, which is substituted for cylinder 4 of the other figures, may be used much the same as in the figures previously described with additional heat being induced also into the belt 35 by the alternating magnetic flux in the cores 3b and 30, etc. Power is fed into the coils 2 in the same manner as in the figures previously discussed. The metal belt 35 is supported on an external metal conductive cylinder 36, thus reducing the total electrical resistance of the belt itself. A feed belt 711, etc., outside the belt 35 and its carrier pulley 36, and aided by guides 33, transports the sheet material into contact with the belt 35. An irradiation shield 35', in the form of an endless band passing around rollers 3, is provided to reduce heat losses. By contrast with the construction in the figures previously described, the paper may be fed into the system with the coated side 5 facing upwardly rather than down so as to place it in direct contact with the hot belt 35.

An apparatus capable of even greater heat capacity is illustrated in FIGURE 10. In this case all the coils 2a, 2b, 2c, 2d, are external, four of them being shown. Each of them energizes a core 3 and each core has one leg 3 passing within the cylinder 4' to give the maximum cross section utilization factor. A separate paper feed system is shown here, using a carrier belt 31 which passes over rolls 32 and between guides 33'. In other respects 8 the apparatus is controlled in the same manner as that of FIGURES l to 3, the guide rollers 16' around the cylinder 4 and the other elements functioning in similar fashion.

What is claimed is:

1. Apparatus for heating non-electrically conductive sheet material comprising, in combination, a rotatable hollow cylinder of high conductivity for heat and electricity, an elongated magnetic flux-generating element comprising two pairs of oppositely disposed cores, each having one leg passing through said cylinder and another leg outside of said cylinder, and a Winding on at least said outer leg having means for supplying alternating current to said winding thereby to induce a magnetic flux in said core, said flux-generating element occupying a major portion of the cross sectional area within said cylinder so as to induce a relatively heavy electric current in the cylinder, and guide means for supporting said sheet material in surface contact with the outer surface of said cylinder.

2. In an apparatus of the character described, the combination of a rotatable hollow cylinder of high conductive metal, movable insulated support means for supporting said cylinder for floating rotation about its axis, means occupying more than half of the cross sectional area within said cylinder for inducing an electric current in the cylinder of suificient magnitude to heat said cylinder to an elevated temperature suitable for heating nonconductive sheet material in contact therewith, and a metal conveying belt for said sheet material surrounding the cylinder to augment the induction effect.

3. In an apparatus of the character described, the combination of a rotatable hollow cylinder of high conductive metal, movable insulated support means for supporting said cylinder for floating rotation about its axis, a means occupying more than half of the cross sectional area within said cylinder for inducing an electric current in the cylinder of sufiicient magnitude to heat said cylinder to an elevated temperature suitable for heating nonconductive sheet material in contact therewith, and at least one additional hollow cylinder in thermal contact with the first named cylinder to augment induction and consequent heat supply.

4. Apparatus for heating non-electrically conductive sheet material comprising, in combination, a rotatable hollow cylinder of high conductivity for heat and electricity, guide rollers supporting said cylinder for rotation about its axis, an elongated magnetic flux-generating element generally co-axial with said cylinder occupying a major portion of the cross sectional area within said cylinder and being sufiicient to induce in said cylinder a relatively heavy electric current, and a guide belt extending around and in contact with substantially the entire periphery of said hollow cylinder, adapted to travel therewith for supporting said sheet material in surface cont act with outer surface of said cylinder around substantially its entire periphery.

References Cited by the Examiner UNITED STATES PATENTS 2,301,589 11/1942 Shepard 219-1061 2,541,416 2/1951 Harrison 219-1061 2,843,712 7/1958 Lillienberg et al. 21910.61 2,953,669 9/1960 Tudbury 21910.61 3,103,571 9/1963 Axelsson et a1. 219-10.61 3,187,150 6/1965 France 21910.61 3,200,230 8/1965 De La Bretoniere 21910.61 3,213,256 10/1965 Munnich 219-1061 RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner.

L. H. BENDER, Assistant Examiner. 

4. APPARATUS FOR HEATING NON-ELECTRICALY CONDUCTIVE SHEET MATERIAL COMPRISING, IN COMBAINTION, A ROTATABLE HOLLOW CYLINDER OF HIGH CONDUCTIVITY FOR HEAT AND ELECTRICITY, GUIDE ROLLERS SUPPORTING SAID CYLINDER FOR ROTATION ABOUT ITS AXIS, AN ELONGATED MAGNETIC FLUX-GENERATING ELEMENT GENERALLY CO-AXIAL WITH SAID CYLINDER OCCUPYING A MAJOR PORTION OF THE CROSS SECTIONAL AREA WITHIN SAID CYLINDER AND BEING SUFFICIENT TO INDUCE IN SAID CYLINDER A RELATIVELY HEAVY ELECTRIC CURRENT, AND A GUIDE BELT EXTENDING AROUND AND IN CONTACT WITH SUBSTANTIALLY THE ENTIRE PERIPHERY OF SAID HOLLOW CYLINDER, ADAPTED TO TRAVEL THEREWITH FOR SUPPORTING SAID SHEET MATERIAL IN SURFACE CONTACT WITH OUTER SURFACE OF SAID CYLINDER AROUND SUBSTANTIALLY ITS ENTIRE PERIPHERY. 